1. Field of the Invention
The present invention relates to a method of heating image formation sheets, and particularly to a method of heating image formation sheets comprising heat-developing photosensitive material during the heat development of latent images on exposed image formation sheets of different lengths.
2. Description of the Related Art
Image recording devices are known which produce images onto image receiving material. Such image recording devices produce a latent image on a heat developing photosensitive material in the form of an image formation sheet or the like, by exposing it, and develops the image by heating the heat developing photosensitive material. Then, the image recording devices superimpose the heat developing photosensitive material on the image receiving material and press together the photosensitive material and the receiving material. As a result, the image recording devices transfer the image onto the image receiving material.
The heat developing photosensitive material and image receiving material used in this sort of image recording device are cut into given lengths, i.e., sheets (for example, A4 size with a total length of 210 mm, or A3 size with a total length of 420 mm), placed one on the other and then conveyed to a heat developing and transfer part. In this heat developing and transfer part, the two materials are held in a superimposed state while being conveyed for a given time between a heating drum heated to about 90.degree. C. and an endless pressure belt. The heat developing photosensitive material is consequently subjected to heat development, and the image recorded on the heat developing photosensitive material is transferred to the image receiving material.
The heat development of the heat developing photosensitive material which is performed after exposure requires heating for a given time (at least 20 seconds or more). Since, as described above, the heating time is the time it takes for the heat developing photosensitive material (and the image receiving material) to pass through the contact portion (heating portion) on the periphery of the heating drum, the speed at which the heat developing photosensitive material (and the image receiving material) is conveyed is determined on the basis of the length of the portion of contact between the heat developing photosensitive material and the heating drum. When heat developing photosensitive materials (and image receiving materials) have different lengths, therefore, the heating time required for heat development can be secured by conveying the materials while holding them uniformly at the same speed, regardless of the actual lengths of the materials.
Since the heat developing photosensitive material is subjected to heat development while wound around the periphery of the heating drum, the time required for this heat development starts from the moment when the front end of the heat developing photosensitive material is wound around the heating drum and ends when the rear end thereof is separated from the drum. In other words, although the time required for heating the heat developing photosensitive material may be 20 seconds or more, as described above, there is a disadvantage in that a time longer than this is required for completing the heat development.
In this case, since the time required for heating the heat developing photosensitive material is determined, the time required for performing the whole of the heat development cannot be reduced by merely changing the length of the contact portion (portion to be heated) on the periphery of the heating drum or by increasing the speed at which the material is conveyed.
In view of the above-described facts, it is an object of the present invention to provide a method of heating image formation sheets, comprised of heat developing photosensitive material, which is capable of reducing the time required for heat developing images exposed on these image formation sheets while enabling better development results of longer image formation sheets.